1. Field of the Invention
The invention relates to the field of control devices and methodologies for controlling emergency sirens and in particular to a control device and methodology which automatically sweeps a siren through a plurality of siren sounds.
2. Description of the Prior Art
Ambulance, fire engines, police and other emergency sirens commonly employ a variety of siren sound patterns for various purposes. These sound patterns typically differ in the frequencies and range covered as well as the timing of frequency variations. For example, the sound pattern normally thought of as the classic "wail" starts at 500 Hz, slowly rises to about 1650 Hz and then even more slowly returns to 500 Hz in a period of approximately five seconds. The European "high-low" sound alternates between a low tone of 650 Hz and a high tone of 1300 Hz with a period of about 0.5 second at each tone.
Periodically alternating between two or more different siren sounds has been found to be a more startling stimulus to bystanders and other drivers than simply using a single sound pattern. It has been found, for example, that wail and even the more rapid "yelp", which is a quickly repeated wail, becomes monotonous and provides a much lower stimulus when continually repeated.
For this reason, drivers of emergency vehicles frequently alternate between two or more sounds such as "wail", "yelp", and "hi-low". However, current methodologies require a rather cumbersome manual switching between sounds by turning a rotary switch, pressing pushbutton switches, or by depressing a horn ring as described in greater detail in "Emergency Vehicle Siren Switching Apparatus," U.S. Pat. No. 3,868,684 (1975), and "Emergency Vehicle Audio Warning System," U.S. Pat. No. 4,040,050 (1977).
Such manual switching of the siren sounds distracts the operator from attention which he should otherwise be directing to the control of the vehicle. As can be readily understood, manually manipulating variations in siren sounds through a rotary switch, pushbutton switches or even by tapping a horn ring is distracting to the operator, who is concentrating on difficult and potential dangerous traffic congestion.
Therefore, what is needed is a circuit and methodology which provides the benefits of switching a siren through a plurality of siren sounds without being subject to the defects or distractions required by prior art systems.